Tests: Appease sanitizer (#3121).

include/verilated.h

@@ -542,6 +542,7 @@ public:  // But for internal use only
 
     // Internal: Check magic number
     static void checkMagic(const VerilatedContext* contextp);
+    void selfTestClearMagic() { m_magic = 0x2; }
 };
 
 //===========================================================================

test_regress/t/t_wrapper_del_context_bad.cpp

@@ -13,7 +13,9 @@ int main(int argc, char** argv, char** env) {
     // Create contexts
     VerilatedContext* contextp{new VerilatedContext};
 
-    delete contextp;  // Test mistake - deleting contextp
+    // Ideally we'd do this, but then address sanitizer blows up
+    // delete contextp;  // Test mistake - deleting contextp
+    contextp->selfTestClearMagic();
 
     // instantiate verilated design
     std::unique_ptr<VM_PREFIX> topp{new VM_PREFIX{contextp, "TOP"}};